Mangroves and coral reefs are rarely, 

 if ever, in close proximity because of 

 their divergent physio-chemical require- 

 ments, but seagrasses freely intermingle 

 with both communities. Seagrasses also 

 form extensive submarine meadows that fre- 

 quently bridge the distances between reefs 

 and mangroves. Seagrass beds of the larger 

 mangrove-lined bays of the Everglades and 

 Ten Thousand Island region, while being a 

 small proportion of the total bottom cov- 

 erage of these bays, are the primary zones 

 where important juvenile organisms, such 

 as shrimp, are found. 



There are two major internal pathways 

 along which the energy from seagrasses is 

 made available to the community in which 

 they exist: direct herbivory and detrital 

 food webs. In many areas a significant 

 amount of material is exported to adjacent 

 communities. 



Direct grazing of seagrasses is con- 

 fined to a small number of species, al- 

 though in certain areas, these species may 

 be quite abundant. Primary herbivores of 

 seagrasses in south Florida are sea tur- 

 tles, parrotfish, surgeonfish, sea ur- 

 chins, and possibly pinfish. In south 

 Florida the amount of direct grazing 

 varies greatly, as many of these herbi- 

 vores are at or near the northern limit of 

 their distribution. The greatest quandry 

 concerns the amount of seagrass consumed 

 by the sea turtles. Today turtles dre 

 scarce and consume a quantitatively insig- 

 nificant amount of seagrass. However, in 

 pre-Columbian times the population was 

 vast, being 100 to 1,000 times - if not 

 greater - than the existing population. 



Some grazers, such as the queen 

 conch, appear to graze the leaves, but 

 primarily scrape the epiphytic algae on 

 the leaf surface. Parrotfish preferen- 

 tially graze the eoiphytized tips of sea- 

 grass leaves, consuming the old portion of 

 the leaf plus the encrusting epiphytes. 



The detritus food web has classically 

 been considered the main path by which the 

 energy of seagrasses makes its way through 

 the food web. Although recent studios 

 have pointed to increased importance of 

 grazing in some areas (Ogdon and Zienan 

 1977), this generalization continues to be 

 supported. 



When assessing the role of seagrass- 

 es, sediment stabilization is also of key 

 importance. Although the seagrasses them- 

 selves are only one, or at most three spe- 

 cies, in a system that comprises hundreds 

 or thousands of associated plant and ani- 

 mal species, their presence is critical 

 because much, if not all, of the community 

 exists as a result of the seagrasses. In 

 their absence most of the regions that 

 they inhabit would be a seascape of un- 

 stable shifting sand and mud. Production 

 and sediment stabilization would then be 

 due to a few species of rhizophytic green 

 algae. 



1.2 CLIMATIC ENVIRONMENT 



South Florida has a mild, semitropi- 

 cal maritime climate featuring a small 

 daily range of temperatures. The average 

 precipitation, air temperature, surface 

 water temperature, and surface water sa- 

 linity, for Key West are given in Table 1. 

 Water temperature and salinity vai'y sea- 

 sonally and are affected by individual 

 storms and seasonal events. Winds affect- 

 ing the area are primarily mild southeast 

 to easterly winds bringing moist tropical 

 air. Occasional major storms, usually 

 hurricanes, affect the region on an aver- 

 age of every 7 years, producing high winds 

 and great quantities of rain that lower 

 the salinity of shallow waters. Puring 

 the winter, cold fronts often push through 

 the area causing rapid drops in tempera- 

 ture and high winds that typically last 4 

 to 5 days (Warzeski 1977, in Multer 1977). 

 In general, summer high temperatures are 

 no higher than elsewhere in the State, but 

 winter low temperatures arc more moderate 

 (Figure 3). 



Water temperatures are least affected 

 on the outer reef tract where surface wa- 

 ters are consistently mixed with those 

 from the Florida Current. By contrast the 

 inner regions of Florida Bay are shallow 

 and circulation is restricted. Thus water 

 temperatures here change rapidly with sud- 

 den air temperature variations and rain. 

 Water temperatures in Pine Channel dropped 

 from 20° to 12°C (68° to 54°F) in 1 day 

 foil owing the passage of a major winter 

 storm (Zieman, personal observation). 

 These storms cause rapid increases in sus- 

 pended sediments because of wind-induced 



